A circuit breaker breaks a circuit and prevents the damage of an electric wire or an apparatus when a current with a predetermined value or more flows due to, for example, an overload or a short circuit. The circuit breaker includes a breaking mechanism portion that breaks a circuit with a bimetal when a current with a predetermined value or more flows and a terminal connected to the power supply side or the load side of the breaking mechanism portion. The breaking mechanism portion and the terminal are provided in the case. A stud connected to a power-supply-side line and a stud connected to a load-side line contact and are fixed to a power-supply-side terminal and a load-side terminal, respectively.
FIG. 6 is a diagram illustrating an example of the structure of a contact portion between the stud and the terminal of the circuit breaker.
When the stud 20 is a type (rear surface connection type) in which it contacts the terminal from the rear surface (the attachment surface of the circuit breaker) of the circuit breaker, the stud 20 has a columnar shape and has an end surface 20a contacting the terminal 40. A screw hole 23 is formed in the stud 20 so as to extend from the end surface 20a on the axis (for example, see Patent Literature 1).
The terminal 40 is formed by bending a strip-shaped conductive member and has a contact portion 41 contacting the stud 20 at one end of the terminal 40. One surface 41a of the terminal contacts the end surface 20a of the stud 20. A through hole 42 without a thread is formed in the contact portion 41 of the terminal 40.
An insertion hole 2b into which the end of the stud 20 is inserted is formed in the rear surface (the attachment surface of the circuit breaker) of the case 2. The diameter of the insertion hole 2b is designed according to the diameter of the stud 20. The terminal 40 is arranged in the case 2 such that the contact surface 41a faces the insertion hole 2b. The stud 20 is inserted into the insertion hole 2b, the end surface 20a contacts the contact surface 41a of the terminal 40, and the screw 27 is inserted into the through hole 42 of the terminal 40 and the screw hole 23 of the stud 20, thereby fastening and fixing the terminal 40 to the stud 20. A spring washer 28 and a washer 29 are interposed between the head of the screw 27 and the terminal 40.
In many cases, the stud 20 is made of copper with a high thermal conductivity. However, in recent years, in some cases, the material forming the stud 20 is changed to aluminum with a thermal conductivity less than that of copper. In the circuit breaker, the amount of heat transmitted to the bimetal needs to be constant. Therefore, when the thermal conductivity of the stud is changed, it is necessary to design a standard for adjusting the bimetal again. However, there is a limitation in the adjustment of the bimetal. When the amount of heat generated is equal to or more than a predetermined value, it is necessary to increase the diameter of the stud to dissipate heat.
However, as described above, the hole 2b formed in the rear surface of the case 2 is designed according to the diameter of the stud 20. When the diameter of the stud 20 increases, it is difficult to insert the stud into the hole 2b and it is necessary to prepare a separate case.